Cleeves, LaurenBergin, Edwin A.Qi, ChunhuaAdams, Fred C.Oberg, Karin2016-01-212015Cleeves, L. Ilsedore, Edwin A. Bergin, Chunhua Qi, Fred C. Adams, and Karin I. Öberg. 2015. “Constraining the X-ray and cosmic ray ionization chemistry of the TW Hya protoplanetary disk: evidence for a sub-interstellar cosmic-ray rate.” The Astrophysical Journal 799 (2) (January 30): 204. doi:10.1088/0004-637x/799/2/204.1538-4357http://nrs.harvard.edu/urn-3:HUL.InstRepos:24816625We present an observational and theoretical study of the primary ionizing agents (cosmic rays and X-rays) in the TW Hya protoplanetary disk. We use a set of resolved and unresolved observations of molecular ions and other molecular species, encompassing eleven lines total, in concert with a grid of disk chemistry models. The molecular ion constraints comprise new data from the Submillimeter Array on HCO+, acquired at unprecedented spatial resolution, and data from the literature, including ALMA observations of N2H+. We vary the model incident CR flux and stellar X-ray spectra and find that TW Hya's HCO+ and N2H+ emission are best fit by a moderately hard X-ray spectra, as would be expected during the "flaring" state of the star, and a low CR ionization rate, ζCR≲10−19 s−1. This low CR rate is the first indication of the presence of CR exclusion by winds and/or magnetic fields in an actively accreting T Tauri disk system. With this new constraint, our best fit ionization structure predicts a low turbulence "dead-zone" extending from the inner edge of the disk out to 50−65 AU. This region coincides with an observed concentration of millimeter grains, and we propose that the inner region of TW Hya is a dust (and possibly planet) growth factory as predicted by previous theoretical work.en-USJournal Article2016-01-09Cleeves, L.I., Bergin, E.A., Qi, C., Adams, F.C., Oberg, K.I.2016-01-2110.1088/0004-637X/799/2/204